Mortgage Amortization Calculator

What a Mortgage Amortization Schedule Actually Shows

An amortization schedule breaks every single mortgage payment into two pieces, interest and principal, and shows how that split changes over the life of your loan. On a fixed-rate mortgage, your total monthly payment stays the same from the first month to the last, but the mix inside it doesn’t. Interest is calculated on whatever balance you still owe, so early in the loan, when your balance is highest, most of each payment goes to interest and only a small piece actually reduces what you owe. As the balance shrinks, the interest portion shrinks with it, and more of each identical payment starts going toward principal instead. On a typical 30-year, $350,000 loan at 7%, the very first payment runs roughly $2,329, and only about $290 of that goes toward principal, the rest is interest. That ratio flips slowly at first, then faster, over the decades that follow.

The crossover point: when your payment finally works more for you than for the bank

Somewhere in the middle of a long-term loan, there’s a specific month where the principal portion of your payment overtakes the interest portion for good. Before that point, you’re paying more in interest than you’re building in equity from that payment alone; after it, the reverse is true. This calculator finds that exact month for your numbers and calls it out directly, since it’s one of the more concrete, motivating milestones in a mortgage that most calculators never bother to name.

Why extra payments made early save so much more than the same payments made later

Every dollar of extra principal you pay stops accruing interest immediately, for every remaining month of the loan. Pay an extra dollar in year one and it stops generating interest for 29 more years; pay that same extra dollar in year twenty-five and it only avoids five years of interest. That’s the entire mechanism behind why modest extra payments made consistently and early can cut years off a 30-year mortgage and save tens of thousands of dollars, even when the extra amount itself looks small next to the loan balance.

Biweekly payments: the one-extra-payment trick, explained precisely

Switching to a biweekly schedule means paying half your normal monthly payment every two weeks instead of the full amount once a month. Because a year has 52 weeks, that works out to 26 half-payments, the equivalent of 13 full monthly payments instead of 12, one extra payment a year that you likely won’t even notice in your day-to-day budget. On a $300,000 loan at 7%, that single extra payment a year can pay off the loan roughly six years early and save tens of thousands of dollars in interest, without requiring any lump sum or a higher monthly commitment. The toggle above models this directly against your own numbers.

How to Read This Calculator’s Results

• The chart shows two lines crossing. The interest line starts high and falls; the principal line starts low and rises. Where they cross is your crossover point.
• The donut shows the lifetime split. On a 30-year loan at today’s typical rates, total interest paid over the full term often approaches or exceeds the original loan amount itself, which is exactly why the extra-payment and biweekly tools above matter.
• The yearly schedule stays collapsed by default on purpose. A 30-year loan has 360 individual payments; loading all of them at once slows the page for no real benefit. Expand only the specific year you actually want to inspect.
• The payoff date reflects your actual first payment month. It’s for planning purposes only and doesn’t change any of the underlying math.

Common Mistakes People Make Reading an Amortization Schedule

• Assuming a lower monthly payment always means less total interest. A 30-year term has a lower payment than a 15-year term on the same loan, but pays substantially more total interest over the full life of the loan.
• Forgetting that extra payments must be applied to principal, not just paid. Sending extra money to a lender without specifying it should reduce principal can result in it being held as a future payment instead, which does nothing to the interest math.
• Confusing a biweekly schedule with an accelerated biweekly schedule. A true biweekly plan naturally produces one extra payment a year through the calendar; an accelerated biweekly plan intentionally pays a slightly larger amount to reach the same result faster. This calculator models the standard version.
• Not accounting for taxes, insurance, and PMI. This tool focuses on principal and interest specifically; your real monthly mortgage payment is usually higher once escrow items are included.

Frequently Asked Questions

References

• Consumer Financial Protection Bureau, mortgage servicing and payment application guidance – consumerfinance.gov
• Freddie Mac Primary Mortgage Market Survey, weekly national rate averages – freddiemac.com/pmms

Related DexoCalc Tools

This amortization calculator is part of the Mortgage Calculators cluster I am building out on DexoCalc. Use the national Mortgage Calculator for a full monthly payment estimate including taxes, insurance, and PMI, the Mortgage Affordability Calculator to work out your target price range from income and debts first, or one of our state-specific mortgage calculators for exact local property tax figures once you’ve settled on a loan amount here.

This calculator provides estimates for educational purposes only and is not a loan offer, pre-approval, or substitute for advice from a licensed mortgage professional. It models principal and interest only and does not include property tax, homeowners insurance, HOA dues, or PMI. Confirm your actual amortization schedule with your loan servicer. Sources: CFPB, Freddie Mac.